The invention relates to an apparatus for processing sheet material, in particular a bank-note processing machine, in which the sheet material is transported in a transport path through between at least two mutually opposing components of a checking device by a transport band.
The transport band serves for guiding and for pressing the sheet material against opposing transport means and against interjacent guiding paths or checking devices. The transport means usually are transport rolls or transport rollers or a second transport band, which by means of deflection rollers is either guided back directly before and behind the checking device or is guided around the checking device. The transport band or the transport bands may also be replaced by several narrow, flat or round belts.
From DE 29 23 148 A1 it is known to guide the second transport band on deflection rollers in grooves, so that the speed of the sheet material is determined by the first transport band located externally in the deflection direction. The second transport band internally located then merely serves to support the sheet material between adjacent deflection rollers, this support, however, may instead also be achieved by a light-transmissive glass plate replacing the second transport band, when the sheet material is to be accessible over the entire width for checking purposes.
The first transport band performing guiding and pressing function in the region of the checking device, however, impedes the carrying out of a transmission measurement at the sheet material. A soiling measurement is also impeded, because for such a measurement the sheet material usually has to be illuminated from both sides. Hence, the first transport band usually is divided into portions and replaced by several narrow belts spaced apart from each other and extending in parallel side by side in the transport direction. But, however, also with this a measurement of the sheet material over its full area and over its entire width and for both surfaces of the sheet material is impossible. The positions of the belts are rather perceived as dark longitudinal stripes upon the evaluation of e.g. transmitted light or ultrasound.
From EP 1 663 829 B1 it is known to guide the transport band or the belts forming the transport band around the checking device and to grasp the sheet material by means of clamp rings to allow the sheet material to be safely transported through the checking device and to enable a check of both surfaces of the sheet material over the full area or in transmission in a manner undisturbed by the transport band.
It has turned out, however, that with sheet material of poor quality, in particular with limp sheet material or sheet material having tears, transport malfunctions, e.g. jams, may occur more often when the check over the full area known from the prior art is performed.